Sustained free chlorine-releasing polydimethylsiloxane/Ca(ClO)2 materials with long-lasting disinfection efficacy

A novel sustained chlorine-releasing polydimethylsiloxane/Ca(ClO)2 (PDMS/Ca(ClO)2) material was fabricated by encapsulating Ca(ClO)2 in a PDMS matrix due to its high hydrophobicity and high chemical stability, which showed immediate-responsive and long-lasting antibacterial capabilities in aqueous conditions. Free chlorine could be released from the PDMS/Ca(ClO)2 after immersion in water for 2 min and could also be sustainedly released for 2 weeks, while the released concentration is negatively related to the duration time and positively with the initial Ca(ClO)2 contents. Additionally, Ca(ClO)2 powder as a filler significantly affects the crosslinking and pore size of PDMS. The PDMS/Ca(ClO)2 materials exhibited enduring antibacterial performance against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) in both planktonic and multispecies-biofilm status. It is expected that this PDMS/Ca(ClO)2 material and its similar composite would be promising candidates for wide sustainable disinfection applications in biomedical and industrial fields.


Introduction
Chlorine-based disinfectants are one of the earliest types of chemical disinfectants used by humans. 1 Based on free chlorine, chlorine-based disinfectants possess strong oxidative properties.In light of their attributes encompassing broadspectrum antimicrobial efficacy, 2,3 cost-effectiveness, 4 and user-friendliness, 2 chlorine-based disinfectants showcase a wide range of applications, spanning from healthcare, 5 environmental disinfection, 6,7 and water purication 8,9 to safeguarding food integrity 5,[10][11][12] and beyond.
Because harmful microorganisms are ubiquitous and have amazing reproductive capacity, which leads to the need for the use of disinfectants over and over again.Sustained-release type disinfectant agents could reduce the need for frequent administration, provide long-lasting antibacterial protection, save time and effort, avoid toxicity at high initial doses, and thus have great application potential in diverse elds.For example, by employing controlled-release mechanisms with minimal antibacterial agents, sustained-release antibacterial pads have achieved extended antibacterial effectiveness and prolonged the shelf life of cold fresh pork. 11The concentration of inorganic chlorine-based disinfectants (such as NaClO, Ca(ClO) 2 ) in water drops rapidly, 13 and in order to make the disinfectant work for a long time, Ca(ClO) 2 tablets 14 or polymers-carried chlorine disinfectants [15][16][17][18][19] have been developed.For instance, Huang, 17 et al. developed a novel biobased chlorine-based sanitizer by encapsulating chlorine-binding polymer in a biobased yeast cell wall particle microcarrier, which could release free chlorine for only about 50 min.At present, some shortcomings including short sustained release time 17,18 and complex preparation process 16 have limited the widespread use and mass production of sustained-release chlorine-based disinfectants.It is important to explore novel strategies to enhance and prolong chlorine-based disinfectant release proles for effective microbial control.
At present, a concerned method of sustained release of water-soluble drugs/reagents is mainly to encapsulate them in hydrophobic polymers.Among them, polydimethylsiloxane (PDMS) is a silicon-based polymer commonly used in numerous biomedical 20 and industrial applications. 21,22Given to the presence of surface-oriented methyl groups from the dimethylsiloxane moiety, the surface of PDMS is highly hydrophobic but still allows slow water penetration. 23,24Therefore, encapsulating substances that are prone to react with water in a PDMS matrix can effectively slow down their reaction rate and prolong the reaction time.As a specic example, researchers have successfully developed a range of oxygen-producing materials by blending solid calcium peroxide with PDMS for tissue engineering studies. 25Additionally, PDMS is strictly chemically stable and does not react with chlorine oxidizers. 26Meanwhile, we chose Ca(ClO) 2 as a chlorine source since Ca(ClO) 2 boasts exceptional stability in its solid state, facilitating convenient storage and transportation.Free chlorine is supposed to be leisurely produced as a result of the Ca(ClO) 2 -H 2 O reaction. 27herefore, we introduced a novel PDMS/Ca(ClO) 2 composite material as a sustained-release chlorine disinfectant product.Firstly, the physicochemical properties of the synthesized materials were characterized by scanning electron microscopy (SEM), wettability assay, and so on.Subsequently, the release performance of Ca(ClO) 2 from PDMS was systematically evaluated by N,N-diethyl-p-paraphenylenediamine (DPD) method, and Inductively Coupled Plasma Optical Emission (ICP-OES) Spectromete for a continued 2 weeks.Furthermore, we specically investigated the long-lasting antibacterial activity of the PDMS/Ca(ClO) 2 system against common pathogenic bacteria in both planktonic and biolm forms.

Preparation of PDMS/Ca(ClO) 2
The PDMS (SYLGARD™ 184 silicone elastomer kit, Dow Corning) is a two components system consisting of prepolymer A (contains: dimethyl siloxane, dimethylvinylsiloxy-terminated; dimethylvinylated and trimethylated silica; ethylbenzenne) and crosslinker B (contains: siloxanes and silicones, dimethyl, methyl hydrogen; dimethyl siloxane, dimethylsioxy-terminated; dimethylvinylated and trimethylated silica).A vinyl-terminated PDMS with a platinum (Pt)-based catalyst and methyl hydrogen siloxane are the main functional components of prepolymer A and crosslinker B, respectively.The prepolymer A and the crosslinker B was mixed at a 10 : 1 weight ratio.And then different contents (0%, 2%, 4%, 6% w/v) of Ca(ClO) 2 powders (available chlorine content: 28-32%, Fuchen Chemical, China) were added and poured into different molds (24well tissue culture plates with a diameter of F15.6 mm per well, 12-well plates tissue culture plates with a diameter of F22.1 mm per well, 6-well plates tissue culture plates with a diameter of F34.8 mm per well) to prepare materials with the same volume (400 mL per well) but different surface areas.Then PDMS/ Ca(ClO) 2 mixture was vacuumed to remove air bubbles and cured at 50 °C for 3 hours.PDMS/Ca(ClO) 2 samples with different contents of Ca(ClO) 2 powders (0%, 2%, 4%, 6% w/v) were referred to as PDMS, P/C-2, P/C-4, P/C-6 respectively.
2.2 Physicochemical properties of PDMS/Ca(ClO) 2 2.2.1 Rheological properties.The rheological properties of the samples were determined using a rheometer (HAAKE © Viscotester iQ).The storage modulus (G 0 ) and loss modulus (G 00 ) were measured at shear rates ranging from 0.01 Hz to 10 Hz at a temperature of 25 ± 2 °C.
2.2.2 Scanning electron microscope (SEM) and energydispersive X-ray (EDX) mapping.A scanning electron microscope (SEM, Inspect F, FEI, and Thermo Fisher Apreo 2C, USA) was used to observe the surface morphology of different groups.The spatial distribution of powder particles within the PDMS matrix aer curing has been characterized by EDX mapping.All the samples were gold sputtered and then the analyzing procedures were carried out.
2.2.3 Wettability assay.Drop Shape Analyzer (DSA30, KRUSS, German) was employed to measure the static contact angles and determine the surface wettability by the sessile drop method.To ensure reliability, we conducted a minimum of three measurements at different locations on both the PDMS and PDMS/Ca(ClO) 2 surfaces with varying concentrations of Ca(ClO) 2 .Water, in the form of 2 mL drops, was utilized as the liquid medium in all of these contact angle experiments.
2.2.4 Brunauer, Emmett and Teller (BET).The N 2 adsorption/desorption isotherms were obtained using a Micromeritics Tristar 3000 adsorption analyzer at liquid nitrogen temperature under a continuous adsorption condition.Prior to testing, the samples were degassed under a vacuum at 120 °C for at least 6 hours.The specic surface area of the samples was calculated using the Brunauer, Emmett, and Teller (BET) method based on the adsorption data, and the average pore size of PDMS/Ca(ClO) 2 samples was calculated using the Barrett-Joyner-Halenda (BJH) model based on the adsorption branch of the isotherm.

Measurement of free chlorine and Ca 2+ generation from PDMS/Ca(ClO) 2
To assess the sustained generation of free chlorine, the primary component of chlorine-based disinfectants, from PDMS/ Ca(ClO) 2 materials, an N,N-diethyl-p-paraphenylenediamine (DPD, Aladdin, China) assay was conducted, which is the most common analytical method for the determination of free chlorine in water. 28Briey, PDMS/Ca(ClO) 2 materials prepared in different molds with varying Ca(ClO) 2 contents (2% and 4% w/v) were soaked in ddH 2 O (1 mL, RT) separately while being protected from light.Firstly, the short-term release performance of the PDMS/Ca(ClO) 2 samples prepared in 24-well tissue culture plates was evaluated by testing the free chlorine within 20 min.Long-term (14 days) release of free chlorine from the PDMS/ Ca(ClO) 2 samples prepared in different molds was also evaluated.In detail, every two days, the soaking solutions from each group were collected completely.The collected solutions were then diluted with ultrapure water, and 50 mL of DPD solution (10 mM) was mixed with 1 mL of diluted solution from each sample.Subsequently, the optical density (OD) value of the mixture was measured at 324 nm to evaluate the free chlorine sustained generation of the PDMS/Ca(ClO) 2 samples.The coloration or tint of the samples may provide insights into the free chlorine sustained generation in the PDMS/Ca(ClO) 2 samples.
The Ca 2+ concentrations in the soaking solutions were tested by ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometer, PE Avio 200, USA).Simply put, the experimental procedure involves placing P/C-2 and P/C-4 samples prepared in 24-well tissue culture plates in individual containers containing 1 mL of ddH 2 O.These containers will be kept in a light-shielded environment at room temperature.At regular intervals of two days, the soaking solution will be collected from each container, and a fresh 1 mL of ddH 2 O will be added for further soaking.

The antibacterial activity in planktonic forms
Staphylococcus aureus (S. aureus) and Escherichia coli (E.coli) were cultured separately in brain-heart perfusion (BHI) liquid medium at 37 °C with shaking at 200 rpm overnight.Prior to use, the bacteria were centrifuged and diluted to 10 5 CFU mL −1 .To evaluate the antimicrobial properties of the material, PDMS/ Ca(ClO) 2 materials prepared in 24-well tissue culture plates were used in this part.And four groups were set as follows: (1) control group (400 mL 0.9% saline), (2) PDMS, (3) P/C-2, (4) P/C-4.Then, 1 mL of bacterial suspension is co-cultured with the PDMS/Ca(ClO) 2 samples from each group and soaked on different days (0, 4, 7, 14 days)in 12-well plates.Aer incubation for 12 h at 37 °C, the culture solutions were transferred into sterilized tubes and diluted 10 5 times with PBS solution, and 20 mL of the bacterial suspension was coated onto 1/3 Soybean Casein Digest Agar Plate (TSA plate, HuanKai Microbial Co., Ltd, China) TSA plates.Subsequently, the plates were incubated for another 24 h at 37 °C before counting the bacteria CFU and taking photographs.S0, S4, S7, and S14 indicate that the samples were soaked in ddH 2 O for 0, 4, 7, and 14 days.
In order to observe the morphological alteration of bacteria, the bacteria aer co-culturing with PDMS/Ca(ClO) 2 samples for 12 h were xed for 2 h at RT with 2.5% glutaraldehyde.The samples were then dehydrated using a gradient of ethanol solutions and nally observed by SEM.

The antibacterial activity in biolm forms
To evaluate the antibacterial activity in biolm forms, E. coli and S. aureus were co-cultured on a titanium disc to obtain a dual-species biolm.Briey, E. coli and S. aureus were diluted separately with Brain Heart Infusion Broth (BHI Broth, Solarbio, China) to a concentration of 10 5 CFU mL −1 .Subsequently, 500 mL of each bacterial suspension was inoculated onto the surface of titanium discs and allowed to form biolms at 37 °C for 48 hours.In order to improve the biolm's adhesion, 1% (w/v) sucrose was added to the bacterial medium.Meanwhile, PDMS/Ca(ClO) 2 samples prepared in 24-well tissue culture plates which were soaked in ddH 2 O (1 mL) for 7 days were dried at real temperature.The biolm-coated titanium discs were then co-cultured in PBS with each group of PDMS/Ca(ClO) 2 samples prepared, respectively, for 12 hours at 37 °C.Aer treatment, the titanium discs were rinsed with saline three times.Live and dead bacteria were stained with a LIVE/DEAD™ BacLight™ Bacterial Viability Kit (Thermo, USA) and visualized using confocal laser scanning microscopy (OLYMPUS FV1200, Japan).The antibacterial rates were calculated using Image J.

Statistical analysis
All data obtained were described as mean ± standard deviation (SD).With the help of GraphPad Prism version 8.0.2 for Windows, one-way ANOVA was used for statistical analysis.The probability value (p-value) < 0.05 was considered statistically signicant.Statistical signicance: *p < 0.05, **p < 0.01, ***p < 0.001.Unless otherwise specied, there are three parallel samples in each experimental group.

Results and discussion
3.1 Fabrication and characterization of the PDMS/Ca(ClO) 2 materials The synthetic route for the fabrication of the PDMS/Ca(ClO) 2 samples was illustrated in Fig. 1a.The PDMS prepolymer A was mixed with Ca(ClO) 2 powder at different concentrations (0%, 2%, 4%, and 6% w/v) along with the crosslinker B, and the mixture was vacuumed and cured at 50 °C for 3 hours.As shown in Fig. 1b, PDMS, P/C-2, and P/C-4 changed from a uid to a solid state, indicating a complete crosslinking.In contrast, it can be observed that the P/C-6 sample did not fully solidify, suggesting that the excessive addition of Ca(ClO) 2 powder affected the crosslinking of PDMS.This may be due to the strong alkalinity of Ca(ClO) 2 , which might disrupt the Si-H bonds of crosslinker B and prevent subsequent hydrosilylation crosslinking reactions between Si-H bonds (crosslinker B) and vinyl groups of siloxane (prepolymer A), 29 though further veri-cation of this hypothesis is required.
Furthermore, the rheological properties of the samples were determined using a rheometer.The storage modulus (G 0 ) and loss modulus (G 00 ) are presented in Fig. 1c.Compared with the PDMS sample, the P/C-2 sample showed no signicant change and the P/C-4 sample exhibited a lower G 0 .Moreover, The G 0 and G 00 values of the P/C-6 sample showed that G 0 was lower than G 00 with increasing shear rate, also indicating the material exhibited liquid-like characteristics. 30herefore, in the subsequent experiments, only P/C-2 and P/C-4 samples were chosen.
The PDMS sample displayed a typical colorless and transparent appearance.Aer adding Ca(ClO) 2 , the P/C-2 and P/C-4 samples showed a milky white color and a decrease in transparency as the content of Ca(ClO) 2 increased (Fig. 1d).Additionally, from the graph, it is observed that Ca(ClO) 2 powders are generally uniformly distributed within the PDMS matrix.
The SEM results (Fig. 2a) revealed that the surface of the PDMS sample is exceptionally smooth and compact.On the surfaces of the P/C-2 and P/C-4 samples, the presence of Ca(ClO) 2 particles can be observed.
The spatial distribution of powder particles within the PDMS matrix aer curing has been characterized by EDX mapping (Fig. 2b).From Fig. 2b, it can be observed that both Ca and Cl are evenly distributed in the PDMS matrix, and in P/C-4, the Cl and Ca are signicantly higher than in P/C-2.
A water contact angle test was employed to assess the wettability of the samples.The results in Fig. 2c revealed that all the samples were hydrophobic.However, compared with the PDMS group, the contact angles of P/C-2 and P/C-4 samples were slightly reduced.This could be probably attributed to the hydrophilic and dissolvable Ca(ClO) 2 particles exposed on the PDMS surface.Next, as depicted in Fig. 2d, analysis of the N 2 adsorption-desorption data revealed that the PDMS/Ca(ClO) 2 samples exhibit a well-structured mesoporous morphology.The average pore size of PDMS, P/C-2, and P/C-4 samples (Fig. 2e) was calculated to be about 8.3 nm, 6.4 nm, and 14.1 nm, respectively.These ndings suggest that the incorporation of 2% Ca(ClO) 2 into the PDMS matrix has decreased the pore size of PDMS and 4% incorporation caused an increase.This may be due to the powder acting as a ller, lling the pores of PDMS and thereby reducing porosity when incorporating 2% Ca(ClO) 2 into the PDMS matrix.However, at 4% incorporation, the normal cross-linking of the PDMS matrix may be affected due to two reasons.One aspect involves the physical space obstruction caused by powders, 31 while the other aspect pertains to the disruption of Si-H bonds in the crosslinker B due to the strong alkalinity of Ca(ClO) 2 , 29 leading to an unexpected increase in porosity.

Monitoring of free chlorine release, pH values and Ca 2+ release
The hydrolysis of Ca(ClO) 2 primarily yields ClO − and Ca 2+ .The reaction primarily involves two processes: The release of free chlorine from PDMS/Ca(ClO) 2 samples in short and long duration was detected using the DPD method.The results (Fig. 3a) showed that free chlorine can be released quickly within 2 min from both PDMS/Ca(ClO) 2 groups prepared in 24-well tissue culture plates.In addition, the cumulative release amount of free chlorine increased over time during 20 min' monitoring.The P/C-4 sample released more free chlorine than P/C-2, which was consistent with the amount of added Ca(ClO) 2 .
Fig. 3b showed that free chlorine could be sustainedly released for about 14 days for both of the two groups from 24well tissue culture plates and the P/C-4 group released more and seemed to last longer.Moreover, it can be noted that the average released concentration was positively related to initial Ca(ClO) 2 contents and also gradually decreased with time.The cumulative release amount of free chlorine aer 14 days (Fig. 3f) depicted that the total release concentration for the P/C-4 sample was about three-fold higher than that of P/C-2.It is notable for proposing that the high chemical stability of PDMS also avoids the assumption of free chlorine by the PDMS matrix.Meanwhile, release curves of free chlorine from the discs prepared in different molds (Fig. 3c) showed that under the premise of identical PDMS volume and Ca(ClO) 2 content, a larger surface area corresponds to a faster and more abundant release of free chlorine within a 14 days period.Hence, we can tailor materials with diverse Ca(ClO) 2 concentrations and surface areas to meet specic application demands.
The pH values of the soaking solution (ddH 2 O) from materials prepared in 24-well tissue culture plates for 2-14 days are shown in Fig. 3d.In the P/C-2 and P/C-4 groups, although the pH initially exceeded 10 on day 2, it maintained a weak alkaline condition with pH values between 7-8.5 across the subsequent test period.The relatively mild alkalinity is environmentfriendly and benecial for safe application.According to literature, 32 the ratio of different types of free chlorine species including ClO − , HClO, and Cl 2 is pH-dependent.Under pH 10, ClO − is the most predominant, while at pH values 7-8.5, a small portion of HClO exists.It is also reported that HClO possesses stronger antimicrobial activity compared with ClO − . 33he release of Ca 2+ from PDMS/Ca(ClO) 2 samples was detected by ICP-OES.As shown in Fig. 3e, the amounts of Ca 2+ were about 200 mg L −1 and 100 mg L −1 on day 2 for P/C-4 and P/ C-2 samples, respectively.Then, the concentration sharply decreased to about 40 ppm on day 4 and remained at ∼10 ppm till day 14.This further conrmed that Ca(ClO) 2 in PDMS/ Ca(ClO) 2 samples reacted with water and released the reaction products.

The long-term antibacterial activity in planktonic forms
To investigate the long-term disinfection activity of PDMS/ Ca(ClO) 2 in planktonic forms, S. aureus and E. coli were selected as test organisms.The antibacterial efficacy of the PDMS/ Ca(ClO) 2 samples was evaluated using the CFU counting method.As shown in Fig. 4a, the bacterial suspension was cocultured with PDMS/Ca(ClO) 2 samples, which were soaked in 1 mL ddH 2 O for 0, 4, 7, and 14 days in order to mimic the different service durations.As shown in Fig. 4b, the antibacterial rates of P/C-2S0 and P/C-2S4 samples were about 70% against S. aureus and those of the P/C-2S7 and P/C-2S14 samples were about 20-40%.The P/C-4 samples exhibited a stronger antibacterial effect against S. aureus than P/C-2.The P/C-4S0, P/ C-4S4, and P/C-4S7 samples exhibited antibacterial rates close to 100%.Even aer 14 days of soaking in water, the antibacterial rate of the P/C-4S14 group was still ∼99.68%.In contrast, the PDMS samples had no antibacterial effect, similar to the control group.
The antibacterial data of E. coli are displayed in Fig. 4d and e.Generally, the antibacterial rates of the samples against E. coli are lower compared with S. aureus.The antibacterial rates of P/ C-2S0 and P/C-2S4 samples were about 20% against S. aureus and those of the P/C-2S7 and P/C-2S14 samples had weak antibacterial ability.Notably, the P/C-4S0, P/C-4S4, and P/C-4S7 samples exhibited antibacterial rates close to 99.7%.Even for the P/C-4S14 samples, it exhibited an antibacterial rate of ∼24.7%.This difference is probably attributed to the surface charge and structure of the bacteria.Gram-negative bacteria typically carry a negative charge on their surface, while Grampositive bacteria, like S. aureus, carry a positive charge.In an alkaline environment, free chlorine exists mainly as negatively charged ClO − , favoring interactions with the negatively charged surface of Gram-negative bacteria.Besides, the thinner cell walls of Gram-positive bacteria, are more susceptible to oxidation and damage. 34In contrast, Gram-negative bacteria possess more complex cell walls with a lipid bilayer and lipopolysaccharide layer, providing antioxidative and exclusion properties that render them less susceptible. 35,36SEM images (Fig. 4f and g) showed the morphology alteration of the bacteria aer different treatments, which were generally consistent with the above CFU results.In comparison to the control and PDMS groups, S. aureus treated with P/C-4 exhibited noticeable rough shrinkage in morphology, while the bacterial morphology of the P/C-2 group showed slight deformation and roughness.The overall trend of morphological changes in E. coli was similar to that of S. aureus, but it showed minor cell rupture.

The long-term disinfection activity in biolm forms
The antibacterial activity against biolms formed on titanium discs was further evaluated using Live/dead staining and CLSM observation.The schematic illustration of the preparation of dual-species biolm (E. coli and S. aureus) and experimental design is shown in Fig. 5a.In order to exhibit the long-term effects, all the used samples were soaked in ddH 2 O for 7 days and dried before follow-up antibiolm experiments.The trends observed were consistent with the antibacterial activity data obtained from planktonic cultures (Fig. 3).As shown in Fig. 5b  and c, the P/C-4S7 group exhibited the highest antibacterial ratio against the mixed biolm (∼97.8%),followed by the P/C-2S7 group with an antibacterial ratio of ∼45.5%.The pure PDMS samples showed no antibacterial effect.Furthermore, upon analyzing the biolm thickness (Fig. 5d), it was observed that the P/C-2 and P/C-4 samples exhibited signicantly thinner biolm compared to the PDMS samples, suggesting that the samples could also eliminate biolm extracellular polymeric substances (EPS) in some extent.
The study showcases a meaningful achievement, as the utilization of PDMS/Ca(ClO) 2 composite materials allows for the sustained release of free chlorine for long-term disinfection or antibacterial applications.Free chlorine can be rapidly released aer being immersed in water, also satisfying immediateresponse requirements.The antibacterial results robustly established its enduring antimicrobial capabilities to both Gram-positive and Gram-negative bacteria.It is worth pointing out that the preparation procedure of PDMS/Ca(ClO) 2 materials is rather simple and environmentally friendly, benecial for industrial production and wide use.Besides, due to the excellent processability of PDMS, this material can be processed into various shapes, such as membranes, spheres, sheets, etc., to meet different application requirements.Nonetheless, in the future, it is essential to address the issue that higher Ca(ClO) 2 contents lead to the uncrosslinking of PDMS, so as to enhance the exibility and concentration-adjustability of the system.We rmly assert that the PDMS/Ca(ClO) 2 materials have great promise in diverse applications, such as but not limited to disinfection for cistern water 37 and dental unit waterlines. 38dditionally, this work proposed a novel sustained-release disinfectant design by utilizing the unique silicone rubberbased polymer PDMS, which might shed light on wider research and product development potentials for diverse disinfectants and silicone materials.

Conclusion
In this study, we have demonstrated the generation of free chlorine-releasing composite materials through a simple combination of PDMS and Ca(ClO) 2 .The Ca(ClO) 2 incorporated within the PDMS matrix exhibits sustained and slow reactions with water in aqueous environments, resulting in a continuous release of free chlorine for 2 weeks.Moreover, the PDMS/ Ca(ClO) 2 composite retained effective long-term antibacterial activity in both planktonic and biolm forms.Considering these promising results, we believe that PDMS/Ca(ClO) 2 material holds great potential for various applications such as water treatment and medical elds as a novel sustained-release disinfectant.

Fig. 1
Fig. 1 Preparation and characterization of PDMS/Ca(ClO) 2 materials.Schematic illustration of the preparation of the materials (a).Photographs (b) and rheological properties (c) of PDMS/Ca(ClO) 2 samples in glass bottles with different concentrations of Ca(ClO) 2 before and after crosslinking.Photographs of PDMS/Ca(ClO) 2 samples (d).

Fig. 3
Fig. 3 Assessment of sustained release capability.Release curves of free chlorine from the discs prepared in 24-well tissue culture plates (F15.6 mm per well) within 20 minutes (a) and over 14 days (b).Release curves of free chlorine from the discs prepared in 24-well tissue culture plates (F15.6 mm per well), 12-well plates tissue culture (F22.1 mm per well), and 6-well plates tissue culture plates (F34.8 mm per well) over 14 days (c).The pH variation curves in the soaking liquids from the discs prepared in 24-well tissue culture plates (d).Ca 2+ release curves from the discs prepared in 24-well tissue culture plates (e).The cumulative Ca 2+ and free chlorine release amount over 14 days (f).(ns indicates no significance, *p < 0.05, **p < 0.01, ***p < 0.001).